In recent years various plastic materials have been used in the production of many medical appliances and analytical instruments.
At the same time, oligodynamic active substances such as proteins and glycoproteins isolated from animals and plants are under intensive studies for their application and development as drugs.
For stabilization or prevention of inactivation of these oligodynamic active substances, various stabilizers have heretofore been proposed. However, in administering the oligodynamic active substances, a problem arises in that there is a considerable difference between the activity as initially indicated and the practical effect obtained on administering the oligodynamic active substances in prescribed dosages.
This means, for example, that dosages to be administered to patients can not be precisely controlled and expensive drugs available only in small amounts are not used effectively.
As a result of extensive investigations to overcome the above-described problems, it has been found that the active substances are adsorbed onto the inner walls of, for example, test tubes, tubes, syringe cylinders, and bottles for nutrient fluids, which are made of glass or plastic materials such as polyethylene, polypropylene, and polystyrene, of medical appliances or analytical instruments, and that this adsorption is sometimes such that the percentage of the active substances being adsorbed reaches about 90%.
To prevent this adsorption phenomenon, silicone treatment has been applied or surface active agents have been used. These procedures, however, have disadvantages in that the effect is insufficient and their use as additives for drugs is not desirable.
At present, urokinase separated and purified from urine or cultured liquor of kidney cells and streptokinase collected from cultured liquor of Streptococci are plasminogen activators employed in practical use as thrombolytic agents.
However, since urokinase and streptokinase have poor affinity for fibrin, it is frequently necessary to administer urokinase and streptokinase in large amounts in order to obtain the required effect on treatment. When large doses are administered, side effects such as gastro-internal hemorrhage are manifested.
Further, plasmin formed in the circulating blood is likely to combine with a plasmin inhibitor in the blood, thereby losing activity rapidly. Therefore, in order to obtain the desired therapeutic effects, it is necessary for the enzymes to be administered in such large amounts as to result in the formation of plasmin in amounts exceeding that of the plasmin inhibitor contained in the blood. When, however, the plasmin is formed in such large amounts, the plasmin decomposes fibrinogen, causing side effects such as hemorrhage. On the other hand, those substances possessing high affinity for fibrin and capable of forming plasmin on the fibrin could decompose fibrin without being affected by the plasmin inhibitor contained in the circulating blood even when used in small amounts and would have only a reduced action to decompose fibrinogen present in the circulating blood.
Under such circumstances, a thrombolytic agent having high affinity for fibrin and high thrombolysing activity when administered in a small dose and having only a low level of side effects such as causing a gastro-internal hemorrhage has been eagerly sought.
As these plasminogen activators, tissue plasminogen activators (hereinafter referred to as "t-PA") present in tissues such as human or animal uterus, kidney, lung, small intestine, foreskin, and blood vesel walls, in culture liquors of normal cells originating from the foregoing tissues, or in culture liquors of tumor cells originating from the foregoing tissues or culture media of microorganisms or mammalian cells having t-PA-producing efficacy by genetic engineering have received increasing attention and are developed as thrombolytic agents. One of the present inventors has succeeded in obtaining t-PA from a tissue culture liquor of normal human tissue derived cells (European Patent Application (OPI) No. 0100982). Further, he has found that there are two types of t-PA: one having a single-chain structure and the other having a double-chain structure, and has reported that although there is almost no difference between the single-chain t-PA and the double-chain t-PA with respect to plasminogen activator (PA) activity and properties, the two forms of t-PA are different from each other in hydrolysis activity with the synthetic substrate t-butoxycarbonyl-phenylalanyl-serylaryginyl-methylcoumarine (Boc-Phe-Ser-Arg-MCA), and furthermore that the two forms of t-PA are different from each other in that upon reduction, the double-chain t-PA is decomposed, whereas the single-chain t-PA remains substantially undecomposed.
In addition, the present t-PA is more similar to t-PA found in the human body than those originating from animal tissues or tumor tissues and, therefore, is useful as a thrombolytic agent.
However, the present inventors' further investigations have revealed that with the present t-PA the same adsorption phenomenon to laboratory and medical equipment as described above occurs, thereby reducing the activity of the t-PA. It is therefore necessary to eliminate the problem of the adsorption phonomenon.
As a result of extensive investigations to discover a stabilizer which can be added to t-PA for use as a thrombolytic agent, it has been found that when purified gelatin is used, the adsorption can be prevented almost 100% and, furthermore, the active component adsorbed can be released and recovered. It has further been found, as a consequence of a study on the effect of the purified gelatin to prevent the adsorption of t-PA, that the purified gelatin acts to prevent the conversion of the single-chain t-PA into the double-chain t-PA.